The term "lanolin" refers collectively to refined products ranging from about 36.degree. to about 44.degree. C. in melting point and obtained from wool grease (WG) which is the lipid secretion of the sebaceous glands of sheep by subjecting the grease to an acid treatment and deacidifying, decolorizing, deodorizing and like processes. Lanolin has emollient, self-emulsifying and like characteristics, closely resembles human sebum, has been dermatologically found to be of safety and has long been in prevalent use as a base material for application to the skin in the field of cosmetics, pharmaceuticals, etc. Lanolin further has a very complex composition consisting primarily of mixtures of esters of almost 100 kinds of lanolin fatty acids and more than 70 kinds of lanolin alcohols and containing up to about ten-odd % of free alcohols with sterols, several % of carbohydrates and traces of free fatty acids. It is said to be a unique lipid among other natural lipids. The lanolin fatty acids constituting lanolin (esters) include straight-chain acids in a small amount of up to about 10% of the whole amount and iso, ante-iso and like branched-chain fatty acids in an amount of about 2/3 of the whole, the remainder of about 1/3 being hydroxy fatty acids. These fatty acids range widely from 9 to 34 in the number of carbon atoms and have an average molecular weight of about 320. Further alicyclic alcohols such as cholesterol and triterpene alcohols which are predominantly lanosterol account for about 70% of all the lanolin alcohols, the balance being aliphatic alcohols chiefly including straight-chain, iso and ante-iso alcohols and further including about 5 to about 8% of diols. These alcohols range from 14 to 33 in the number of carbon atoms and about 370 in average molecular weight.
On the other hand, with the development of agricultural chemicals such as pesticides and a rapid increase in the amount of demand therefor in recent years, the raw material for lanolin, i.e., WG, contains residues of such pesticides, which are left almost unremoved by the process presently practiced for refining WG. Thus, pesticide residues are found also in the product lanolin.
The pesticide residues present in lanolin are a wide variety of pesticides which are in common use and which are divided generally into the following organic chloride compounds and organic phosphorus compounds.
Organic chlorine compounds
Hexachlorobenzene (HCB), .alpha.,.beta.,.delta.-hexachlorocyclohexane (.alpha.,.beta.,.delta.-BHC), .gamma.-hexachlorocyclohexane (.gamma.-BHC), aldrin (ALD), dieldrin (DLD), endrin (END), o,p-dichlorodiphenyltrichloroethane (o,p-DDT), p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), p,p'-dichlorodiphenyldichloroethylene (DDE), heptachlor (HC), heptachlor epoxide (HCE), .gamma.-chlordane (.gamma.-CD), etc.
Organic phosphorus compounds
Diazinon (DZN), bromophosethyl (BPE), dichlofenthion (DCP), .alpha.-chlorfenvinphos (.alpha.-CVP), .beta.-chlorfenvinphos (.beta.-CVP), etc.
Each of the pesticides will hereinafter be referred to by the abbreviation.
Although the amounts of pesticide residues in lanolin are dependent on the WG used as the material for lanolin, especially on the history of the greasy wool from which the WG is recovered, the amounts determined by analyzing samples available were in the following ranges.
______________________________________ Amount of pesticide Pesticide Range (ppm) Average (ppm) ______________________________________ .gamma.-BHC 0-22.3 0.96 DLD 0-15 2.27 END 0-2.26 0.24 o,p-DDT 0-5.07 0.57 p,p'-DDT 0-13 1.14 DZN 0-21 17.64 DCP 0-2.24 1.25 BPE 0-2.39 1.33 .alpha.-CVP 0-7.89 3.65 .beta.-CVP 0-8.97 4.62 ______________________________________
The presence of pesticide residues could give rise to serious problems in the use of lanolin with safety. Presently, it is desired to develop methods of removing such pesticide residues.
Although it is ideal to remove all the pesticide residues to levels below detectability, such ideal removal is not required. For example, the standard values given below for edible animal oils and fats such as lard (German regulation values set in 1984) will be referred to as target values (allowable residue values).
______________________________________ Pesticide Target value ______________________________________ HCB 0.5 .alpha.,.beta.,.delta.-BHC 0.3 .gamma.-BHC 2.0 ALD + DLD 0.2 DDT + DDE 3.0 END 0.2 DZN 0.3 BPE 0.05 DCP 0.10 CVP 1.0 ______________________________________
Since no standards are mentioned for DZN, BPE, DCP and CVP in animal oils and fats, corresponding regulation values for foods are given for reference.
However, a very wide variety of pesticides are found to be present in lanolin in very small quantities, and considerable difficulties are expected of the usual refining process if it is employed for removing these pesticides from lanolin and WG which is the material therefor. Moreover, lanolin itself exhibits its inherent properties when in the form of a mixture of the complex composition mentioned above. If the refining process used entails changes in the composition of lanolin, the refined product will invariably exhibit impaired characteristics and become unsuitable for use in cosmetics, pharmaceuticals and the like. Up to date, substantially no measures have been taken for the removal of pesticide residues.
The high-temperature vacuum distillation process and high-temperature steam distillation processes appear useful generally for refining various substances but encounter difficulties when used for removing pesticides from lanolin because the pesticide residues in lanolin generally have a high boiling point and very low vapor pressure and further because organic chlorine compounds are all soluble in fats and have high affinity for lanolin. Additionally, these high-temperature processes rather have the drawback of permitting greatly accelerated degradation and discoloration of lanolin itself.
It appears also feasible to apply the usual solvent extraction process to lanolin, whereas no solvent has been found which is capable of dissolving, extracting and separating off the pesticide residues only without dissolving lanolin.
Although it is known that organic phosphorus compounds are unstable to light and heat and readily undergo hydrolysis in the presence of acids or alkalis, the hydrolysis treatment has the drawback of breaking the ester linkage of lanolin at the same time to inevitably degrade lanolin itself.
It is also known to utilize the adsorption process with activated carbon for removing pesticides, especially organic chlorine pesticides, from aqueous solutions, whereas no effect will be expected of this process if it is applied to lanolin which is a multi-component mixture since activated carbon fails to effect selective adsorption.
Although irrelevant to lanolin, reports have been made to the effect that some pesticides are removable by the hydrogenation process and steam distillation process generally employed for refining and deodorizing edible oils and fats (see "Journal of the Japan Oil Chemists' Society", 23(1), 49-52(1974); J. Amer. Oil. Chem. Soc., 45, 866-869(1968); J. Amer. Oil. Chem. Soc., 46, 482-484(1969); etc.). According to these reports, however, the pesticide removal effect varies considerably with the kind of oils or fats to be treated, while the removable pesticides are limited to a few kinds of pesticides including BHC. Incidentally, edible oils or fats are deodorized by the steam distillation process at a temperature of 200.degree. to 260.degree. C. and at 1 to 30 mmHg over a period of 1 to 5 hours by passing water vapor through the oil or fat in an amount of several % of the oil or fat, but these conditions are very severe to lanolin, cause marked discoloration of the product and seriously impair the commercial value thereof. The principle of steam distillation is that when the sum of partial vapor pressures of substances present has reached 760 mmHg, the substance to be removed evaporates at a temperature lower than its inherent boiling point. Accordingly, the evaporation of the contemplated substance is greatly affected by the vapor pressures of the other substances conjointly present, which greatly vary the removal effect. If the substance to be removed is present along with other substance which is close thereto in vapor pressure, a sufficient removal effect will not be achieved unless a larger quantity of steam is used than otherwise. Free alcohols are present in lanolin which are more closer in vapor pressure to pesticides than the main component esters thereof, so that the process, when applied to lanolin, encounters difficulty in fully removing the pesticides unless a considerably large quantity of steam is released. In this respect, the process appears infeasible.
On the other hand, a process has been proposed for preparing hypo-allergenic lanolin by reducing the free fatty alcohol content of common lanolin to less than 2.5% by vacuum distillation, followed by a treatment with activated clay and subsequent filtration to lower the content of scouring agent to less than 0.05% (see Examined Japanese Patent Publication SHO 60-14796). This process is intended to remove from lanolin allergens which are of course different from pesticide residues. The main component esters of lanolin do not evaporate under the temperature condition of this process but are collected as a residue and therefore undergo marked degradation such as discoloration due to a high temperature. Moreover, the removal of free alcohols by the process results in the disadvantage of giving a lower water uptake (W/U) to the product lanolin. The water uptake is an index indicating the hydrophilic property of lanolin. When having a high water uptake, lanolin is uniformly miscible with water, forming a stable water-in-oil emulsion containing a large quantity of water. Thus, the water uptake is one of the important characteristics of lanolin for use in cosmetics and the like.
In brief, since a wide variety of pesticides remain in very small quantities in lanolin or the like which exhibits its original properties when in the form of a mixture of complex composition, it has been extremely difficult to remove these pesticide residues from lanolin or the like without altering the composition thereof and further without impairing the characteristics of lanolin suited for use in cosmetics, pharmaceuticals, etc.
An object of the present invention is to provide a novel process for refining lanolins by removing pesticide residues from the lanolin to levels lower than the allowable limits thereof without impairing the original characteristics of the lanolin to ensure improved safety, i.e., to provide a process for preparing highly refined lanolins.